'\" te
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.TH PROFIL 2 "Nov 12, 2001"
.SH NAME
profil \- execution time profile
.SH SYNOPSIS
.LP
.nf
#include <unistd.h>

\fBvoid\fR \fBprofil\fR(\fBunsigned short *\fR\fIbuff\fR, \fBunsigned int\fR \fIbufsiz\fR, \fBunsigned int\fR \fIoffset\fR,
     \fBunsigned int\fR \fIscale\fR);
.fi

.SH DESCRIPTION
.sp
.LP
The \fBprofil()\fR function provides CPU-use statistics by profiling the amount
of \fBCPU\fR time expended by a program. The \fBprofil()\fR function generates
the statistics by creating an execution histogram for a current process. The
histogram is defined for a specific region of program code to be profiled, and
the identified region is logically broken up into a set of equal size
subdivisions, each of which corresponds to a count in the histogram.  With each
clock tick, the current subdivision is identified and its corresponding
histogram count is incremented. These counts establish a relative measure of
how much time is being spent in each code subdivision.  The resulting histogram
counts for a profiled region can be used to identify those functions that
consume a disproportionately high percentage of \fBCPU\fR time.
.sp
.LP
The \fIbuff\fR argument is a buffer of  \fIbufsiz\fR bytes in which the
histogram counts are stored in an array of \fBunsigned short int\fR. Once one
of the counts reaches 32767 (the size of a \fB short int\fR), profiling stops
and no more data is collected.
.sp
.LP
The \fIoffset\fR, \fIscale\fR, and  \fIbufsiz\fR arguments specify the region
to be profiled.
.sp
.LP
The \fIoffset\fR argument is effectively the start address of the region to be
profiled.
.sp
.LP
The \fIscale\fR argument is a contraction factor that indicates how much
smaller the histogram buffer is than the region to be profiled. More precisely,
\fIscale\fR is interpreted as an unsigned 16-bit fixed-point fraction with the
decimal point implied on the left. Its value is the reciprocal of the number of
bytes in a subdivision, per byte of histogram buffer. Since there are two bytes
per histogram counter, the effective ratio of subdivision bytes per counter is
one half the scale.
.sp
.LP
The values of \fIscale\fR are as follows:
.RS +4
.TP
.ie t \(bu
.el o
the maximum value of  \fIscale\fR, \fB0xffff\fR (approximately 1), maps
subdivisions 2 bytes long to each counter.
.RE
.RS +4
.TP
.ie t \(bu
.el o
the minimum value of  \fIscale\fR (for which profiling is performed),
\fB0x0002\fR (1/32,768), maps subdivision 65,536 bytes long to each counter.
.RE
.RS +4
.TP
.ie t \(bu
.el o
the default value of  \fIscale\fR (currently used by  \fBcc \fR\fB-qp\fR),
\fB0x4000\fR, maps subdivisions 8 bytes long to each counter.
.RE
.sp
.LP
The values are used within the kernel as follows:  when the process is
interrupted for a clock tick, the value of  \fIoffset\fR is subtracted from the
current value of the program counter (pc), and the remainder is multiplied by
\fIscale\fR to derive a result. That result is used as an index into the
histogram array to locate the cell to be incremented. Therefore, the cell count
represents the number of times that the process was executing code in the
subdivision associated with that cell when the process was interrupted.
.sp
.LP
The value of \fIscale\fR can be computed as  (\fIRATIO\fR \fB* 0200000L\fR),
where \fIRATIO\fR is the desired ratio of  \fIbufsiz\fR to profiled region
size, and has a value between 0 and 1. Qualitatively speaking, the closer
\fIRATIO\fR is to 1, the higher the resolution of the profile information.
.sp
.LP
The value of \fIbufsiz\fR can be computed as
(\fIsize_of_region_to_be_profiled\fR \fB* \fR\fIRATIO\fR).
.sp
.LP
Profiling is turned off by giving a \fIscale\fR value of 0 or 1, and is
rendered ineffective by giving a \fIbufsiz\fR value of 0. Profiling is turned
off when one of the \fBexec\fR family of functions (see \fBexec\fR(2)) is
executed, but remains on in both child and parent  processes after a
\fBfork\fR(2). Profiling is turned off if a \fIbuff\fR update would cause a
memory fault.
.SH USAGE
.sp
.LP
The \fBpcsample\fR(2) function should be used when profiling dynamically-linked
programs and 64-bit programs.
.SH SEE ALSO
.sp
.LP
.BR exec (2),
.BR fork (2),
.BR pcsample (2),
.BR times (2),
.BR monitor (3C),
.BR prof (7)
.SH NOTES
.sp
.LP
In Solaris releases prior to 2.6, calling \fBprofil()\fR in a multithreaded
program would impact only the calling \fBLWP\fR; the profile state was not
inherited at \fBLWP\fR creation time. To profile a multithreaded program with a
global profile buffer, each thread needed to issue a call to \fBprofil()\fR at
threads start-up time, and each thread had to be a bound thread. This was
cumbersome and did not easily support dynamically turning profiling on and off.
In Solaris 2.6, the \fBprofil()\fR system call for multithreaded processes has
global impact \(em that is, a call to \fBprofil()\fR impacts all
\fBLWP\fRs/threads in the process. This may cause applications that depend on
the previous per-\fBLWP\fR semantic to break, but it is expected to improve
multithreaded programs that wish to turn profiling on and off dynamically at
runtime.
